There are known injection devices of this kind in which a movable support for the syringe can be tensed against the action of a spring and can be held back by means of a pawl. In these, a thrust member is provided which is displaceable to perform the injection by bearing upon the piston rod of the syringe after the injection needle is shot into the skin by manipulation of a release lever, so that the injection proceeds in a single course of movement. It cannot be controlled and cannot be interrupted, however. It is furthermore known in the case of the so-called automatic injection machines to leave the pushing ahead of the piston and the piston rod of the syringe completely to the pull of a finger, or to interpose a hydraulically-operated bellows. In both cases, the injection procedure is removed from the movement and the feeling of the finger. Which of these is selected depends to a considerable extent on the dexterity and and sensitiveness of the user's finger. With release and movement of the syringe support, the danger is not excluded that the needle, especially in the event of purely mechanical transmission, may give way.
With regard to the controllability of the injection procedure, the known injection devices that seek to provide control have rather expensive and complicated mechanisms which consist of many parts, whereby the injection device is relatively expensive and also susceptible to trouble. Moreover, these injection devices are suitable only for use for one specific syringe design, e.g. only one rather small syringe. With this, the user is referred to performing the injection two or more times when larger volumes are required, which is extremely disadvantageous and bothersome. Moreover, the known injection devices do not cater to the possibility of varying the depth of puncture for the injection needle, although the desired depth depends upon the individual concerned and where the puncture is to be effected on him or her.